Students in the United States whose household income is less than 130% of the poverty line qualify for free lunch, and students whose household income is between 130% and 185% of the poverty line qualify for reduced-price lunch. Education researchers and policymakers often use free and reduced-price lunch (FRPL) status to measure socioeconomic disadvantage. But how valid is this measure? Linking IRS income tax data to school administrative records for all eighth graders in one California public school district and Oregon public schools, we examine how well FRPL enrollment captures student disadvantage. We find that FRPL categories capture relatively little variation in household income. However, FRPL captures elements of educational disadvantage that IRS-reported household income data do not.